Entrained particle fluid flow is well known and can be found in numerous systems in a wide variety of uses. One such example of entrained fluid flow is in the field of particle blasting. With particle blasting, entrained particles are introduced into a flow of a transport fluid, such as a gas, flow through a delivery hose and out a blast nozzle to be directed at a high speed against a workpiece or target in order to achieve a desired result, such as cleaning and surface coating removal. Conventional particle fluid blast media includes sand, plastic beads, walnut shells and even shot peening. Recent years have seen significant growth in the use of sublimable particles, such as carbon dioxide, as the blast media. The use of sublimable particles is accompanied by cryogenic temperatures which typically improve performance. As used herein, the reference to entrained particle flow includes any particles now used or used in the future as blast media.
In many applications, it is necessary to control the direction of the entrained particle fluid flow. Preferably, when space permits, such turning of entrained particle flow is accomplished through large gentle bends in the delivery hose. However, in many applications, space constraints require tight or abrupt turns, such as when the workpiece or target is in an area having restricted access. Examples of this include the cleaning of molds and removal of surface coatings in tight places.
The prior art is virtually devoid of the ability to turn entrained particle fluid flow abruptly and efficiently. Abrupt directional change of entrained particle flow has typically involved sharp radial turns of the delivery hose (or pipe) blast nozzle. Substantial particle-to-particle and particle-to-wall collisions occur when sharp radial turns are present. When turned by such conventional means, typical particle blast fluid media, such as sand or plastic beads, which is relatively durable, do not suffer any significant loss in size or mass from the particle-to-particle or particle-wall contacts. However, significant erosion of the passageway at the outside of the turn typically occurs, creating a high wear area. This requires frequent maintenance to replace the affected component. When the turn of entrained particle flow occurs in a unitarily constructed nozzle, the entire nozzle must be replaced.
In contrast, sublimable blast media, such as carbon dioxide particles, can suffer significant reduction in size and mass due to such particle-to-particle and particle-to-wall collisions present in prior art turns. Since particle blasting performance is directly related to the particle velocity, mass and surface area covered by the blast impact, the blasting performance typically drops dramatically with such reduction of the integrity of individual particles when using conventional abrupt turning designs for sublimable particles.
Thus, there is a need in the art for a device to turn entrained particle flow without significant degradation or deleterious effects to the entrained particles themselves or to the device.
There is a need in the art for a device which can turn an entrained particle fluid flow without significant degradation of the particle size and mass, without significant erosion of the turn component, and correspondingly without significant degradation of overall blasting performance. To achieve this, in accordance with the teachings of the present invention, there is a need to be able to turn an entrained particle fluid flow without significant particle-to-particle contact and particle-to-wall contact. Additionally, there is a need for a device and method for turning entrained particle flow through an abrupt turn.